What causes dust allergy?
Allergies to household dust are common and tend to be worse in winter when houses are sealed up tight against cold weather. All allergies are caused by the reaction of our immune system to molecules called proteins that enter through our lungs, digestive system, or skin. If we eat something we are allergic to our body reacts, often violently. Likewise if we breath something we are allergic to we experience a range of symptoms from a mildly stuffy nose to anaphylactic shock. An allergy to dust is caused by proteins in the dust that we react to when they enter our lungs. The allergy-producing protein (allergen) is in dust because of a tiny mite, the dust mite, that lives in and consumes part of the dust. The allergen is part of the mite's waste products.
Treating dust allergies
The key steps to treating dust allergies are (1) reduce the amount of dust, and allergen, in your environment; (2) reduce the activity of dust mites; (3) medically treat the allergy symptoms.
Dust and allergen can be reduced by normal cleaning, choosing the right the furnishings for a room, and filtering the air to remove allergen particles. It is especially important to reduce the amount of dust and allergen in bedrooms because of the adverse effect these allergies have on sleep quality.
Wet cleaning is much better than dry sweeping or dusting which only serves to stir up dust and the allergen pool. Most types of vacuum cleaners are counter productive as well. Floors and windows should be regularly washed, even the walls and ceiling in the bedroom should be washed yearly. No special soap is needed. The idea is to remove dust and allergens and simple water plus a mild detergent will suffice.
Remove rugs and other dust-trapping fabrics from the bedroom. Furniture should be covered in removable fabric that can be washed at least once a year. Bedding should likewise be washed as often as possible, plus an allergen-proof mattress cover.
Finally, install an air filtering system (air purifier) that employs HEPA-type filters. These filters scrub the air and remove nearly all suspended allergen so it can't enter your lungs. These air filters can be fairly expensive, and expensive to operate, but do reduce the level of allergy-causing allergen in the air stream. See Air Purifiers For Dust Mite Allergy for more information.
Dust mites themselves are nearly microscopic, don't bite and would go largely unnoticed except for the fact that they produce these allergens. You can't effectively treat the mites directly with insecticide but you can slow their development by reducing dampness in the air (humidity), as dry air tends to reduce mite activity. Central heating and air conditioning are very effective. Also, it may help to put a barrier between you and mites that may live in your mattress using an allergen-proof mattress cover.
Very effective allergy therapies are now available. Mild allergies can be treated with OTC medications (respiratory allergy) while more severe allergies can be treated with desensitisation therapy or prescription allergy medications. See your medical professional, get tested for the specific allergen so that it can be managed.